International Journal of Physics and Research (IJPR) ISSN 2250-0030 Vol. 3, Issue 3, Aug 2013, 1-6 © TJPRC Pvt. Ltd. WETTABILITY AND ELECTRICAL PROPERTIES OF Bi-Sn BASED LEAD FREE SOLDER ALLOYS RIZK MOSTAFA SHALABY Metal Physics Laboratory, Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt ABSTRACT Wettability, electrical resistivity and thermo-elasticity of five systems namely, Bi-42wt. % Sn, Bi-40 wt. %Sn-2 wt. % In, Bi-40 wt.% Sn- 2 wt.% Ag, Bi-38 wt.% Sn-2 wt.% In- 2 wt. % Ag and Sn-wt.%37Pb have been investigated and analyzed. The examined physical properties are improved by addition Ag and In at small level, 2 wt. % to the Bi-42Sn based alloy. These improved properties indicate that these alloys are adequate for low temperature soldering applications. Contact angle measurements demonstrated that In and Ag additions improved wetting/spreading performance on Cu; a contact angle of 20.23˚ was observed for Bi-38Sn-2In-2Ag. In this study, the addition of In and Ag decreases the contact angle and hence remarkably improve the wettability. Also the electro-resistivity of Bi-38Sn-2In-2Ag solder alloy is about ρ = 7.8×10 -6 Ω.cm is much lower than that of Sn-37Pb solder. It is recommended that the quaternary Bi-38Sn-2In-2Ag alloy consider as a suitable substitutes for Sn-37Pb traditional solder alloy. KEYWORDS: Small Addition, Electrical Resistivity, Thermo-Elasticity, Longitudinal Strain, Wettability INTRODUCTION The Bi-Sn has recently been considered as one of the lead free solder materials that can replace the Sn-37Pb solder without increasing soldering temperature. Bismuth has also been used as the alloying element in the binary Sn-Bi systems to provide suitable substitutes for Sn-Pb solder alloys. Sn-Bi based alloys are an alternative to replace Pb-based solders in the low temperature ranges [1]. Moreover, the low-temperature Bi-Sn solder alloy has many advantages in special soldering applications, such as the solder joints of temperature-sensitive zones and the outer layers of classification packaging, which can reduce the influence of soldering temperature on the inner layer of classification packaging. In addition Bi-42Sn solder is suitable for hermetic packaging of electronic device and microelectromechanical systems (MEMS) movable parts [2]. Wettability and mechanical properties of Sn-Ag-Bi are described in [3]. It is found that contact angle measurements demonstrated that Bi additions improved wetting/spreading performance on Cu; a minimum contact angle of 31±4 was observed with 4.83 wt. % Bi addition. The measurement of contact angle is used to determine the extent of wetting, which, in turn, is an issue in the reliability of electronic packaging. With the advent of the new Pb-free solder alloys, there is a renewed interest to evaluate the contact angles of the proposed alloys as a measure of their wettability. The experimental assessment of the solder wettability can be used to predict the performance of the new solder alloys. The wetting-balance [4] and sessile-drop techniques [5-7] have been extensively used to measure the contact angles in order to determine wettability. However, there are still few wettability data for the Pb-free solders. As one of the most promising candidates of the Pb-free solder alloys, Sn-Bi-Xternary systems have been studied in mechanical properties and interfacial reactions between solders and substrates. The purpose of this study is to investigate the wetting behavior of the Bi-Sn Pb-free solder by measuring the contact angles on the copper substrate. The wetting behavior of a new Sn-Bi-Cu Pb- free solder on Cu substrate was investigated by sessile drop method an Ar-H2 flow in the temperature range from 493 K to 623 K was studied [8]. The results show that 69.5Sn-30Bi-0.5Cu exhibits good wettability on Cu substrate. Variation of